Let us, for example, again take a vessel of the present build, and compare it with that of its predecessor of ten years ago, which I have already described.

Fig. 48 is the cross midship-section of a vessel of the present build, and clearly shows the improvements which

Fig. 48.

have been effected. The sectional areas of the

upper deck

of this vessel, which is of the same size as the preceding,

are as follows:

Open trough-plates on deck, and plates on each side, as
before, to a depth of six feet under the deck

Square inches.

where the area is larger than before, and the strength, although still deficient on the deck, would be increased from 3800 to 4200 tons, which is much in favour of the security of the ship.

Taking another vessel (fig. 49) of still more recent con

Deck-planking, say

Total area

85.8

. 432.0

h, by formula, assuming the bottom section to be in ss of the top, would give 4600 tons as the distributed

Fig. 49.

ing weight for a smaller vessel. This is, however, short of the required proportion, and admits of furimprovement, as we shall presently show.

ving now directed attention to existing defects in onstruction of iron vessels, I may venture to proceed

to the more important consideration of their removal, by passing from a system of apparent guesswork to a careful adherence to sound principles in design, like those established by direct experiment for other constructions governed by the same laws and subject to the same strains. If I am correct in treating iron vessels in the light of simple girders, I shall be able to show a better disposition of material, calculated to remedy present defects, and greatly increase the strength of vessels, without any great increase of cost, to resist transverse strains. If I were proceeding upon theoretical considerations, the results I have stated might be doubted; but we have a sufficient number of experiments upon hollow wrought-iron girders to calculate the strength and resisting powers of ships to transverse strain, with a near approximation to accuracy in the results.

Let us, therefore, again take the case of a vessel 306 feet long, 41 feet 6 inches beam, and 26 feet 6 inches deep, built according to Lloyd's rules as an Al vessel of the highest class, for twelve years, from dimensions given in Table G. In such a vessel we have the best known construction, according to the highest authority, and although I do not wish to find fault, or in any way question the regulations of Lloyd's, which appear to have been drawn up with great care, yet I am of opinion that they may be greatly improved upon by the following alterations. Let us suppose the vessel to have a displacement of 5600 tons, and to be constructed with a midship-section exactly similar to what is required in the regulations of Lloyd's. In this section (shown in fig. 48), not only is the deck section defective in its resistance to a tensile or compressive strain, when compared with the bottom, but following up these rules, as laid down for the guidance of builders, two very important points seem to require revision, namely, the they make the strength of materials in vessels to be

proportion to their tonnage, without reference to their length, and also that they require the plating, stringers, and frames at the ends of the vessel to be about the same weight and strength as at midships. Now it is at the latter part where the strength is required, as in every case the strain is greatest there, and gradually diminishes towards the stem and stern. In fact, the section of the plates and stringers ought to be double at midships, both at the deck and the bottom of a well proportioned ship.

To illustrate these facts, it will be necessary to estimate the strength of a vessel constructed according to the latest regulations of Lloyd's, for the highest class, Al vessels, and then to point out the distribution of material which will secure perfect uniformity of strength.

Taking the length at 306 feet, beam 41 feet 6 inches, depth 26 feet 6 inches, we have the sectional areas :

Again, if we take the sectional area of the deck and six feet down the sides (which is a fair average of its powers of resistance to tension and compression), and allowing 130 square inches of iron as an equivalent for timber-stringers, deck-planking, &c., the area will be as under :